Malgus surviving fatal injuries, then the ensuing explosion of the space station which had a ridiculously upgraded power core(including Rakata and Gree tech) and then an unknown length of time exposed to space vacuum is probably a better feat than either of his opponents can shake a stick at.
Arcann tanking the Force Lightning Storm of Valkorion-the excess of which penetrated the shields of every ship in the vicinity of the spire, critically damaging them and killing all life onboard-until a second more powerful blast overwhelmed him and knocked him out, sending him falling unconsciously thousands of feet and surviving it all, before becoming more powerful is beyond either of them too.